This invention relates to an improved means for protecting semiconductor devices and, particularly, logic devices which have been premounted on printed circuit boards, from the effects of static electrical charges or other phenomena causing differences in potential across exposed terminals of the board.
The need for protection of semiconductor devices, such as MOS and C-MOS integrated circuits, from the deleterious effects of static electrical charges has long been recognized. A discussion of the matter may be found in a publication of the Solid State Division of RCA entitled, "Digital Integrated Circuits, Application Note ICAN-6000" and subtitled, "Handling and Operating Considerations for MOS Integrated circuits" by S. Dansky and R. E. Funk. Further, U.S. Pat. No. 4,019,094 granted to Dinger et al on Apr. 19, 1977 describes in detail the problems involved and provides a solution in the form of a clip assembly for attachment to individual semiconductor packages. The clip assembly electrically short circuits the leads of the package and thereby prevents the buildup of a static charge on the active elements of the semiconductor which might cause damage thereto.
Other examples illustrative of means for protecting semiconductor devices per se are disclosed in U.S. Pat. Nos. 3,648,108 granted to R. J. Bailey, 3,653,498 granted to T. W. Kisor, 3,746,157 granted to T. C. I'Anson, 3,774,075 granted to A. L. Medesha and 3,908,153 granted to G. C. Cason, Jr.
The shorting clips or devices disclosed in the cited prior art are intended to be resiliently maintained in positive registration with the semiconductor package, thus leaving the lower ends of the package leads, such as for DIP packages, free in order that the clip may remain on the package throughout normal handling and assembly operations prior to insertion and soldering the leads in respective apertures of a printed circuit board.
The deleterious effects of static electrical charges upon semiconductor devices continue to be a problem even after the semiconductor devices are permanently attached to the boards. That is, physical contact by a worker whose body has accumulated a static charge may, in all likelihood, damage one or more of the devices mounted on an unprotected printed circuit board just as in the cases of the package per se. In the matter of printed circuit boards, it will be apparent that these boards are designed to be inserted and replaced in connecting receptacles, such as edge board connectors or the like. The present invention contemplates the provision of continuity of protection for the various semiconductor devices mounted on a respective board before being inserted in and after it has been removed from the connecting receptacle.